Methods for installing shoulder rings in threaded pipe couplings

ABSTRACT

A shoulder ring, for installation in a threaded pipe coupling between the installed pin ends of two pipes being connected by the coupling, has opposing end faces and a central opening, and may be lobate or circular in shape. The shoulder ring provides enhanced axial retention within the coupling by incorporating a thread element which engages the internal threads of the coupling to prevent or deter displacement of the ring from the coupling. Alternatively, enhanced axial retention may be provided by way of an interference or interlocking fit that is plastically induced during the ring installation process. The shoulder ring may be of lobate or circular configuration, with the axial retention of lobate embodiments being further enhanced by forces acting radially outward against the coupling due to elastic deformation of the ring during installation. Also disclosed are tools for installing the shoulder rings in a threaded coupling.

FIELD OF THE INVENTION

The present invention relates to couplings for joining tubular members,and in particular to shoulder rings for enhancing the torque capacity ofsuch couplings. In addition, the invention relates to tools forinstalling shoulder rings in threaded couplings.

BACKGROUND OF THE INVENTION

Tubulars used to drill and complete bore holes in earth materials aretypically joined by threaded connections. Numerous threaded connectiongeometries are employed to provide sealing and load-carrying capacitiesto meet drilling, installation and operating requirements. Of thesegeometries, tapered pipe threads are among the simplest and most widelyused.

Within the context of petroleum drilling and well completion, wells aretypically constructed by drilling the well bore using one tubularstring, largely made up of drill pipe, then removing the drill pipestring and completing by installing a second tubular string, referred toas casing, which is subsequently permanently cemented in place. Thetubular strings are formed by connecting lengths of pipe, referred to asjoints, with threaded connections. With this traditional method of wellconstruction, both the drill pipe and casing joint designs areseparately optimized for the different performance requirements of thedrilling and completion operations respectively. More specifically, thedrill pipe connections must accommodate torque required to drill, whichis not required during completion.

Recent advances in drilling technology have enabled wells to be drilledand completed with a single casing string, eliminating the need to‘trip’ the drill pipe in and out of the hole to service the bit and makeroom for the casing upon completion of drilling. This change ismotivated by potential cost savings arising from reductions in drillingtime and the expense of providing and maintaining the drill string, plusvarious technical advantages, such as reduced risk of well caving beforeinstallation of the casing.

However, using casing to both drill and complete the well changes theperformance requirements of the casing string, and more particularly thetorque capacity of the casing connections, from those establishedthrough use within the traditional methods of well construction.

The most widely used of casing connections are the industry standardthreaded and coupled buttress (BTC) and 8-round (LTC or STC) connectionshaving tapered pipe thread geometries specified by the AmericanPetroleum Institute (API). These connections have limited torquecapacity and are thus not well suited to the casing drillingapplication, but are readily available and relatively inexpensive. Tomore fully realize the potential benefit of this emerging casingdrilling system (CDS) technology, it is therefore desirable to findmeans to press these industry standard connections into service byidentifying means to inexpensively increase their torque capacity.

Similar motivations to improve the sealing capacity of connections usingAPI thread forms have led to the invention of apparatus and methods suchas described in U.S. Pat. No. 4,706,997, U.S. Pat. No. 4,878,285, U.S.Pat. No. 5,283,748, U.S. Pat. No. 5,689,871, and U.S. Pat. No.4,679,831. These patents generally describe inventions where a modifiedcoupling, provided with an internal floating sleeve or seal ring, isemployed to join pipes having standard API thread forms on their pinends. The seal ring is positioned in the so-called J-section spacebetween the pin ends of a made-up threaded and coupled connection. Theseal ring internal diameter is approximately matched to the internalpipe diameter and is coaxially placed inside the coupling at itsmid-plane so as to engage both pin ends when the connection is made up.According to the teachings of these inventions, this engagement orshouldering is primarily intended to enhance the seal performance of theconnection beyond that provided by the standard API configuration.Several additional benefits are also obtained, such as improved flowperformance and a smooth-running bore. The use of resilient materials inconjunction with the rigid seal ring or as separate seals is also taughtas a means to further promote sealing.

While these descriptions of the prior art do not explicitly address theutility of such a “convertible metal ring” or seal ring as a means toimprove the torque capacity otherwise available from API connections,the increased torque capacity is a well-known benefit. In fact,manufacturers of such connections quantify this parameter in publishedperformance data such as provided by Hunting Oilfield Services for aproduct described as “the KC Convertible coupling system”.

These prior art implementations of rigid seal rings recognise that thewide tolerance variation allowed for the pin and box geometries ofthreaded and coupled connections meeting API specifications permits acorrespondingly wide range of axial position after make-up, if asatisfactory level of interference or “dimensional control” is to beachieved (see U.S. Pat. No. 5,283,748). Consequently, to obtainsatisfactory “dimensional control”, this prior art teaches thatadditional measures must be taken to reduce the tolerance range of pinsand/or boxes provided for use with seal rings and to control the make-upposition. Such steps include specifically manufacturing “modified boxes”to tighter tolerances than required by API specifications, andpre-screening of product manufactured to API tolerances to similarlyobtain pins and boxes having more precisely controlled geometry. Toensure controlled placement and retention of the seal ring, it is taughtthat additional machining of the coupling's central thread region isrequired to form a seat for the seal ring. To obtain dimensional controlof the so-called mill end make-up position, additional fixtures ormeasurements are required.

However, these prior art couplings require modification of the standardAPI components or increased quality control and, therefore,substantially reduce the benefits of low cost and simplicity originallysought from using existing industry standard couplings and pins. Inaddition, prior art couplings are in large part motivated by the desireto upgrade the pressure containment capacity of API connections and, assuch, are not optimized to obtain the upgraded torque capacity desiredfor casing drilling applications.

U.S. Pat. No. 6,899,356 discloses a floating shoulder ring that may beused to substantially increase the ability of tubular connections totransmit torque. When placed internally between the pipe ends of athreaded and coupled pipe connection, the shoulder ring acts as afloating internal upset coupling shoulder capable of reactingcompressive axial load between the pin ends and thus enhancing theconnection torque capacity. The shoulder ring of U.S. Pat. No. 6,899,356is particularly useful as a means to upgrade the torque capacity oftapered couplings such as, for example, unmodified API buttress andround threaded and coupled connections, manufactured to industrystandard tolerances, to meet the requirements of casing drillingapplications. The shoulder ring is placed substantially coaxially in thecoupling of the connection, between the pin ends of the joined tubulars.

To be most generally useful for these applications, the floatingshoulder ring should be amenable to rapid field installation on jointswith couplings already bucked on (for example, in accordance withexisting procedures as generally specified by API), without damaging theconnection threads. It should be anchored or fixed securely enough toprevent being dislodged or knocked out from loads arising due tohandling and installation operations such as make-up, break-out, orequipment movement in and out of the open-ended casing in the rig floor.In addition, the ring, once installed, should not substantially reducethe minimum diameter (drift diameter) through the connection, whilebeing able to carry generally the maximum axial and torsional loads thatcan be carried by the pin tips to mobilize the full shoulderingpotential of the pin ends.

In general terms, the floating shoulder ring of U.S. Pat. No. 6,899,356may be summarized as comprising a body having a central openingtherethrough, a first end face on the body; an opposite end face on thebody; an inner surface adjacent the central opening and extendingbetween the first end face and the opposite end face and an outersurface extending between the first end face and the opposite end face;the body having a substantially uniform cross-sectional shape betweenthe first end face; the opposite end face, the inner surface and theouter surface; and the ring being shaped such that its radius to theouter surface varies around the outer surface circumference to form aplurality of lobes.

The plurality of lobes define alternating radially-extending peaks andvalleys around the inner surface and the outer surface circumferences.The radial peaks and valleys are contained within two circles havingdiameters referred to as the outer peak diameter and inner valleydiameter. The outer peak diameter is preferably greater than thediameter of the coupling into which the ring is to be installed, so thatwhen placed in a coupling, the peaks engage against the internal surfaceof the coupling with sufficient radial force to frictionally retain thering in place and, coincidentally, to largely elastically deform thering to displace the valleys radially outward and the peaks radiallyinward to force the ring into a generally circular configuration withinthe coupling. Preferably, the circumference of the outer surface isselected to be substantially the same as the inner circumference of thecoupling into which the shoulder ring is intended to be installed.

The ring fits into the J-space between the pin ends in the coupling suchthat the inner surface of the ring is open to the coupled tubing stringbore. In one embodiment, the inner surface circumference is less thanthe internal circumference of the pins and greater than the specified orotherwise required drift for the tubing string in which the ring is tobe used.

The first and opposite end faces form torque shoulders against which thepin ends of pipe lengths may bear, upon application of sufficient torqueacross the connection when the pipe lengths are made up into the boxesof a coupling. When the pin ends of the pipe lengths in the coupling aretorqued against the ring end faces, the forces cause a frictionalresponse on the ring faces and in the threads, so as to react additionaltorque and prevent excess penetration of either of the pins into thecoupling. In one embodiment, the end faces are substantially planarand/or smooth, to facilitate use as torque shoulders.

Preferably, the ring has a length between the first end face and theopposite end face sufficient to permit each of the pins to bear againstthe ring, when they are threaded into the coupling. Preferably, thelength is selected to prevent excess penetration of the pins into theirrespective boxes of the coupling and to maintain the made-up pinposition within the allowable power-tight position range such as thatspecified by API.

It is increasingly common for drill strings, casing strings, andproduction strings to be made up using a pipe-running tool mounted to arotary top drive. Pipe-running tools, of which there are several knowntypes, incorporate means for releasably engaging either the bore orouter surface of a pipe with sufficient strength to transfer the weightof a pipe section (or a pipe string) to the top drive, and to transfertorque from the top drive to a supported pipe section so as to connectit to, or disconnect it from, a pipe string. The specific mechanismsused to engage the pipe vary from one type of tool to the next, but theycommonly incorporate some sort of slips or jaws that can be movedradially outward into gripping engagement with the bore of a pipe (i.e.,internally gripping), or radially inward into gripping engagement withthe outer surface of a pipe (i.e., externally gripping).

To make up a tubular string using an internally-gripping pipe-runningtool, the pipe-running tool is “stabbed” into the box end of a new pipesection that is to be added to the string. The pipe-running tool isactuated to engage and grip the walls of the new pipe section asdescribed above, and the top drive then lifts the new pipe section intoposition above the upper (box) end of the uppermost pipe section in thetubular string being added to. The top drive then lowers the new pipesection so that its bottom (pin) end enters the box end of the uppermostpipe section in the string. Finally, the top drive is rotated to screwthe pin end of the new pipe section into the coupling, therebycompleting the operation of adding the new pipe section to the string.

During break-out operations, this procedure is essentially reversed. Thetop drive lowers the pipe-running tool into engagement with the box endof the uppermost section of pipe in an existing pipe string. Thepipe-running tool is then actuated to grippingly engage the upper pipesection. Then, with the lower portion of the string being restrainedfrom rotation by other means, the top drive is rotated to unscrew theupper pipe section from the rest of the string. The removed pipe sectionis then disengaged from the pipe-running tool and moved to a storagelocation.

When the box end of a pipe section being added to or removed from a pipestring is fitted with a floating shoulder ring in accordance with U.S.Pat. No. 6,899,356, there can be a risk of the shoulder ring becomingdislodged when the pipe-running tool is disengaged. This risk arises, inthe case of an internally-gripping tool, from the possibility of theshoulder ring becoming snagged by the tool's jaws, slips, or otherpipe-engagement means, or, in the case of an externally-grippingpipe-running tool, from the possibility of the shoulder ring becomingsnagged by the stinger that is typically used to sealingly engage theinside of the pipe with seal elements. Irrespective of the type of toolsor equipment used to make up or break-out a pipe string, there is alsothe possibility that a shoulder ring could become dislodged from abox-end coupling when running any tools or equipment into or out of thepipe string, or if the shoulder ring adheres to the pin end of the pipesection above it. The latter condition could arise due to one or morefactors, including metallic or adhesive bonding (perhaps induced bycompression and/or torque during joint make-up), and build-up of foreignmaterials at the interface between the shoulder ring and the pin end ofthe pipe.

If a shoulder ring is dislodged or lost from a pipe coupling, due to oneof the foregoing causes or any other cause, the ring will need to berepositioned or replaced—assuming, of course, that the loss ordislodgement of the shoulder ring is noticed before another pipe sectionis screwed into the coupling. If the dislodgement or loss of theshoulder ring is not noticed, there will be a corresponding reduction inthe torque capacity of the coupling. For these reasons, there is a needfor a shoulder ring of the same general type as disclosed in U.S. Pat.No. 6,899,356, but which provides enhanced resistance to dislodgementfrom a pipe coupling, over and above the resistance afforded by theradial forces exerted by the shoulder ring against the internal surfaceof the coupling due to elastic deformation of the ring duringinstallation. The present invention is directed to this need.

BRIEF DESCRIPTION OF THE INVENTION

In a first aspect, the present invention is a shoulder ring for use inassociation with a threaded coupling between two tubular members,incorporating axial retention means for preventing or restrictingdislodgement of the shoulder ring from the coupling. In a second aspect,the present invention is a shoulder ring installation tool, forinstalling the shoulder ring in a threaded coupling.

In a first embodiment of the shoulder ring of the present invention, theaxial retention means is provided in the form of one or morethread-engaging elements disposed on the outer perimeter of the shoulderring and adapted for threading engagement with the tapering internalthreads of a standard pipe coupling. Whereas a prior art floatingshoulder ring is pushed or pressed into the coupling and held therein byradial forces induced by elastic deformation, the shoulder ring of thefirst embodiment of the present invention is installed, whether byapplied axial load or torque, into the coupling such that itsthread-engaging element or elements will engage the internal threads ofthe field end of the coupling, such that the shoulder ring will resistdisplacement from the coupling in the event of an axial or pryingforcing being inadvertently applied to the ring.

As with the floating shoulder ring of U.S. Pat. No. 6,899,356, theshoulder ring of the present invention may be lobate, in which casesignificant radial contact forces will develop between the ring and thecoupling due to elastic stresses induced in the ring duringinstallation. Persons of ordinary skill in the art will appreciate thatmeans and methods can be readily devised for installing a lobateembodiment of the present invention into the box end of a tubularcoupling can be readily devised, without restricting the scope of theinvention. To provide a non-limiting example of a suitable installationmethod, a lobate shoulder ring may be pressed onto a mandrel so as toelastically deform it into a substantially circular shape prior toinsertion into the coupling, whereupon the mandrel, with shoulder ringin place, may be inserted into the coupling without substantial radialcontact occurring between the ring and the interior surfaces of thecoupling during the installation process. Withdrawal of the mandrel willpartially relieve the induced elastic forces in the ring, such that thering's axial retention means will be urged radially outward intoengagement with the threads of the coupling.

In an alternative installation method, means are provided for gripping alobate shoulder ring of the present invention such that it can berotated into the box end of the coupling, with the ring's axialretention means helically engaging the coupling's tapered internalthreads, and with sufficient torque being applied to the shoulder ringto overcome friction forces that develop between the ring and thecoupling as the ring progresses further into the tapering threadstructure.

Regardless of the installation method used, the shoulder ring enjoys thebenefits of elastically-induced radial forces that develop uponretraction of the installation tool, and these radial forces in factenhance the security with which the thread-engaging elements areretained in the threads of the coupling.

The thread-engaging element or elements of the shoulder ring may takeany of several forms. For example, the circumferential extent of thethread-engaging element can vary. The thread-engaging element could be asingle 360-degree helical thread, or it could take the form of multipleintermittent projections lying on a helical path around the shoulderring. The thread profile of the thread-engaging element may also takedifferent forms, limited only by the practical requirement that it be ofa design that will effectively engage the box thread of the coupling.The thread form is also not limited to a standard full-profile thread,and may have a customized profile modified to optimize elastic range andhoop stiffness, or to facilitate varying installation methods and tools.

In an alternative embodiment of the shoulder ring of the presentinvention, enhanced axial retention is provided in the form of aplastically-induced interference fit or an interlocking fit between theshoulder ring and the internal surface of the coupling. An interferencefit, as the term is used in this patent specification (and as it isgenerally understood in the art), is a fit between two generallycylindrical and coaxially assembled inner and outer parts wherein thecircumference of the inner part (i.e., the shoulder ring, in the presentcontext) tends to be confined by the outer part (i.e., the coupling, inthe present context), resulting in a residual compressive contact stressstate acting between the assembled parts. An interlocking fit is to beunderstood as a geometric relation between the outer surface of theinner part (ring) and inner surface of the outer part (coupling) wherebyaxial movement tending to remove the ring tends to induce or increaseinterference between the parts (thus inhibiting separation of theparts).

In the present case, an interference or interlocking fit may beaccomplished by using a shoulder ring configured to permit readyinsertion into a coupling without deformation or rotation of the ring,and then applying sufficient forces applied radially outward to theshoulder ring to plastically deform the shoulder ring to effect aninterference or interlocking fit with respect to the coupling, whichinterference or interlocking fit restricts axial movement of theshoulder ring inside the coupling. The radial forces for inducingplastic deformation may be applied uniformly or intermittently aroundthe circumference of the ring. The induced plastic deformation may beeither localized or global, and could be in the form of localdeformation of external surface features such as ribs or rougheningasperities provided on the ring.

In accordance with this particular embodiment of the invention, theshoulder ring may incorporate specific geometries and/or materialproperty designs which facilitate general or localized plastic yieldingof the shoulder ring in response to forces acting radially outwardagainst the shoulder ring and correlative forces induced to act betweenthe ring and coupling.

In a further aspect, the present invention is a tool for applyingradially-outward forces against a shoulder ring sufficient to effect aninterference or interlocking fit with internal surfaces of a pipecoupling.

In alternative embodiments, the shoulder ring of the present inventionmay be of non-lobate configuration (i.e., substantially circular), aswill be explained in greater detail further on in this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to theaccompanying figures, in which numerical references denote like parts,and in which:

FIG. 1 is a perspective view of a lobate shoulder ring according to afirst embodiment of the present invention.

FIG. 2 is a top plan view of the shoulder ring of FIG. 1.

FIG. 3 is a sectional view along line III-III of FIG. 2.

FIG. 4 is a partial sectional view through a tubular connection made upusing a shoulder ring in accordance with the present invention.

FIG. 5 is a top plan view of an alternative shoulder ring configuration,having three lobes (amplitudes shown exaggerated) and shown prior toinstallation.

FIG. 6 is a transverse sectional view through a coupling, havinginstalled therein a shoulder ring as in FIG. 5.

FIG. 7 is an enlarged sectional view through a tubular connection,parallel to the axis, and having installed therein a shoulder ring as inFIG. 3.

FIG. 8 is an enlarged sectional view through a tubular connection,parallel to the axis, and having installed therein a shoulder ringaccording to an embodiment of the present invention incorporating alow-profile, low stab flank angle thread form.

FIG. 9 is an enlarged sectional view through a tubular connection,parallel to the axis, and having installed therein a shoulder ringaccording to an embodiment of the present invention incorporating a lowprofile, low stab flank angle thread form.

FIG. 10 is an enlarged sectional view through a tubular connection,parallel to the axis, and having installed therein a shoulder ringaccording to an embodiment of the present invention incorporating a zerolobe design.

FIG. 11 is a partial sectional view, parallel to the axis, through ashoulder ring installation tool incorporating a torque-activatedgripping mechanism.

FIG. 12 is a partial sectional view, perpendicular to the axis of theconnection, through the shoulder ring installation tool of FIG. 11.

FIG. 13 is a partial sectional view, parallel to the axis of theconnection, through a shoulder ring installation tool incorporating afrustoconical gripping surface.

FIG. 14 is a partial sectional view, parallel to the axis of theconnection, through a shoulder ring installation tool incorporating alobed gripping mechanism.

FIG. 15 is a partial sectional view, perpendicular to the axis of theconnection, through the shoulder ring installation tool of FIG. 14.

FIG. 16 is a perspective view of a shoulder ring according to anembodiment of the present invention incorporating a residual radialload-retention mechanism.

FIG. 17 is a sectional view of the shoulder ring of FIG. 16 placed in aninternally taper-threaded coupling, shown prior to plastic deformationby application of outward radial force.

FIG. 18 is a sectional view of shoulder ring of FIG. 16 placed in aninternally taper-threaded coupling, shown after plastic deformation byapplication of outward radial force.

FIG. 19 is a partial sectional view, perpendicular to the axis of theconnection, through a shoulder ring installation tool incorporating amechanism for applying radially-outward forces against a shoulder ring.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

General Concepts

In accordance with the present invention, a shoulder ring is providedfor placement in a threaded and coupled connection, such as a standardAPI connection, joining two lengths or joints of tubulars.

Shoulder Ring with Thread Element

According to a preferred embodiment of the present invention, as shownin FIG. 1, shoulder ring 10 has a mill end face 11 and a field end face12, with an inner surface 13 extending between the mill end and fieldend faces. Outer face 14 of ring 10 has mill end 15 and thread element17 at field end 16. Ring 10 as shown in FIG. 1 has a generally lobateshape; in the embodiment shown in FIG. 1, ring 10 has four lobes 20,with four lobe valleys 21 and four lobe peaks 22. Although it will beappreciated that the shoulder ring of the present invention may have twoor more lobes (or zero lobes) if desired, the shoulder ring preferablyis formed with a plurality of lobes designed to provide an effectivehoop stiffness as required by the application and the diameter of thecoupling in which the ring is to be used. A lobe is defined by radiallyextending peaks with valleys disposed therebetween, such that the radiusvaries about the ring's circumference.

Referring now to FIG. 2, lobes 20 of ring 10 are generally shown to beof uniform configuration and evenly spaced about the ring circumference.It is to be understood, however, that the lobes can be spaced asdesired, and that in the preferred embodiment lobe spacing is varied toachieve hoop stiffness required by the application and to accommodatevariations in the manufacturing process.

Referring now to FIG. 3, ring 10 is shown to be of substantially uniformcross-section 18 around its circumference. As may be appreciated fromFIG. 2, lobes 20 are formed by varying the radius of the ring's innerand outer surfaces, with the geometric centerpoint of the lobestypically being offset from the ring's centerpoint 23.

Referring again to FIG. 2, lobes 20 on shoulder ring 10 can be formedusing numerous manufacturing methods. It has been found that lobateshoulder rings can be cold-formed, by applying radial loads sufficientto permanently deform rings that were originally circular. Fixturing maybe used to ensure substantially uniform radial displacement at allvalleys 21 relative to ring centerpoint 23.

FIG. 4 shows a partial section view of a tubular connection 40, with aninternally taper-threaded coupling 30 having a shoulder ring 10installed therein according to the present invention. Ring 10 ispreferably to be installed so as to be longitudinally centered withincoupling 30. Coupling 30 has outside surface 31 and inside threadedsurface 32, which in this case is shown as a tapered API buttressthread. It is to be understood, however, that the thread form is notlimited to API buttress; in preferred embodiments, ring geometry iscustomized for each specific thread form to provide the maximumincremental torque capacity.

Each of the two sets of female tapered threads of coupling 30 iscommonly referred to as the box. In the process of making up a tubingstring, the pin ends (i.e., male threaded ends) 34′ and 34″ of twojoints of tubing 33′ and 33″ are threaded into boxes 35′ and 35″respectively of coupling 30.

Referring still to FIG. 4, in accordance with typical industry practice,one of the coupling boxes is arbitrarily selected for first make-up. Onepin end 34′ of a tubular joint—which pin end is then referred to as themill end pin—is threaded into the selected box 35′ of the coupling 30.The box 35′ joined to the mill end pin 34′ is referred to as the millend box, and the connection 36′ is referred to as the mill endconnection. As the name suggests, the mill end make-up is commonlycompleted at the pipe mill, and the tubulars thus prepared are shippedfor eventual field assembly into a string for the well. The secondmake-up required for field assembly (the so-called field make-up) joinsthe open male threaded end 34″ (termed the field end pin) to the openbox 35″ on a coupling (termed the field end box). This connection istermed the field end connection 36″.

Referring still to FIG. 4, when ring 10 is placed in the center of amade-up coupling, end faces 11 and 12 act as shoulders or abutmentsurfaces, against which the end face 37′ of the mill end pin 34′ and endface 37″ of the field end pin 34″ can bear upon application ofsufficient torque applied to complete the field end make-up, orsubsequently during operations employing the string in the wellbore tofurther drill or complete the well or to perform other operations. Theshoulder ring thus transmits load between the pin ends 34′ and 34″. Thebearing load thus created on the pin ends, and reacted in the threads,results in an increased frictional capacity capable of resistingrotation and is largely responsible for increasing the torque capacityin the well-known manner of so-called shouldering connections. Thisinteraction between torque and axial load is commonly employed in boltedconnections where applied torque is used to pre-load the bolt and thusapply an axial clamping force. Simultaneously, if the bearing load issufficient to cause pin end faces 37′ and 37″ to come into conformablecontact with end faces 11 and 12 of the shoulder ring 10, shoulder sealsare formed. In the preferred embodiment, end faces 11 and 12 are madesmooth to enhance sealing capabilities between the ring and pin ends.

Referring still to FIG. 4, shoulder ring 10 may be installed in thecoupling 30 anytime prior to stabbing the field end on the rig floor,including immediately prior to mill end make-up. However, ring 10 ispreferably installed in the coupling after the mill end connection 36′is formed, and prior to assembly of the field end connection 36″ on therig floor. This is the least intrusive to existing operational practice,and allows the ring length (i.e., the longitudinal distance between endfaces 11 and 12) to be selected to accommodate variations in mill endmake-up position from the specified API power-tight position.

In certain applications, it is desirable to select the length of thering to control the shoulder position for field end make-up. Theshoulder position is determined by mill end make-up position and ringlength. In tapered connections, radial interference imposed between pinand box is an increasing function of make-up position beyond hand-tight,which in turn establishes the interfacial contact stress in the threadsrequired to effect a thread seal and, particularly in 8-roundconnections, to control joint strength. While sealing capacity andstrength vary with contact stress, so do the likelihood and potentialseverity of galling and thread damage, which are detrimental to threadsealing, load capacity, and reusable life. Depending on the application,improved accuracy in control of make-up induced interference maytherefore be used as a means to better optimize seal and load capacityagainst risk of thread damage and galling. Controlling field endshoulder position can thus be used to provide a more satisfactoryinterference state and may be accomplished as discussed hereinafter.

Referring still to FIG. 4, a variation in the power-tight position ofthe pin within the coupling is referred to as power-tight stand-off, andis the axial distance from the made-up position of the mill end pin 34′to the power-tight plane in the coupling as specified by API. The millend power-tight stand-off may be determined in various ways, but ispreferably obtained by measuring, such as by use of a caliper, thedistance from the end face 37′ of the mill end pin 34′ to the face 38 ofthe coupling field end box 35″ and subtracting one-half the couplinglength and the specified distance between the center of the coupling andthe nominal end of the power-tight plane. (See API Standard 5B,“Specifications for Threading, Gauging and Thread Inspection of Casing,Tubing and Line Pipe Threads”.) The mill end power-tight stand-off thusdetermined may be used to select the length of ring prior toinstallation, so that the standoff can be compensated for, and the fieldend face 12 of the installed ring 10 can be near or at the power-tightplane of the field end box. The appropriate ring length should beselected for each connection. This adjustment is most easilyaccomplished by providing a selection of manufactured ring lengths fromwhich to choose during installation. In casing drilling applications,satisfactory control of the field end position covering the entireallowable range of API tolerances is obtained by providing rings inthree length increments.

Referring now to FIG. 5, which shows an end view of ring 10 a with threelobes 20 a, ring 10 a is shown in the neutral configuration, prior toinstallation in a coupling and with no forces applied thereto. In theneutral configuration, the ring has an effective inner diameter, termedherein the inner valley diameter (D_(inner valley n)), which is thediameter of the circle contacting the innermost point of each of thevalleys 21 a of the ring inner surface 13 a. The neutral ring also hasan effective outer diameter, termed herein the outer peak diameter(D_(outer peak n)), which is the diameter of the circle circumscribingthe outermost point of each of the peaks 22 a of the ring outer surface14 a. The ring outer surface 14 a also defines a circumference, thelength of which equals a circle having the diameter D_(circ). Whenselecting a ring for use in a particular coupling, the diameter D_(circ)is selected to be substantially equal to or greater than the minimumdiameter of the coupling, and the D_(outer peak n) of the ring in theneutral configuration is selected to be greater than the minimumdiameter of the coupling in which the ring is to be installed.

Referring to FIG. 6, installation of the preferred embodiment of thepresent invention is accomplished by threading the ring 10 a into theopen end of a coupling 30 towards the coupling center. As the ring 10 ais forced into the coupling 30, the outer surface 14 a comes intocontact with and develops radial bearing forces against the insidesurface 32 of the coupling box threads. The radial bearing forces aredetermined by the lobe geometry of the ring. The lobes are designed soas to maintain a balance between adequate retention force and ease ofinstallation. As the ring 10 a is advanced towards the center of thecoupling, the outer peak diameter of the ring is reduced as confined bythe decreasing diameter of the tapered box. This causes the radialheight of the lobes 20 a to be reduced such that the ring assumes a morecircular configuration. When the ring is positioned at the couplingcenter the ring has an installed outer peak diameter (D_(outer peak i))close to or the same as D_(circ), as shown in FIG. 6. For illustrationpurposes, the initial amplitude of the lobes and the final gaps 42between the outside surface of valley 21 a and the coupling insidesurface 32 are shown exaggerated in FIGS. 5 and 6.

By comparison between FIGS. 5 and 6, it will be evident that while thecircumference of the ring 10 a is substantially constant in theinstalled ring, the radial forces developed by installation of the ringcause the installed outer peak diameter (D_(outer peak i)) to be lessthan the neutral outer peak diameter (D_(outer peak n)), and theinstalled inner valley diameter (D_(inner valley i)) to be greater thanthe neutral inner valley diameter (D_(inner valley n)). Once installed,a gap 42 may or may not remain between the coupling and the ring outersurface at the valleys 21 a, depending on the actual coupling diameterD_(circ) and plastic flow allowed by virtue of the material from whichthe ring is manufactured.

It is to be understood that although the lobes in the illustratedembodiment are formed such that the valleys are urged radially outwardlywhen the ring is confined within the coupling, the ring can be formedsuch that the valleys are urged radially inwardly during installation.Whether the valleys are urged inwardly or outwardly will depend on theamplitude of the lobes and on the direction along which the stresses areconducted through the ring relative to the apexes of the valleys.

To meet the requirements for some applications such as casing drilling,the ring is preferably selected such that D_(inner valley i) of theinstalled ring is less than the inner diameter of the pins and greaterthan the specified or otherwise required drift diameter for the tubingstring in which the ring is to be used. It is preferred that the finalinner diameter be less than the inner diameter of the tubing, so thatthe pin ends tend to not deform inwardly as readily when they bearagainst the ring at the upper limit of the system torque capacity. Inaddition, for applications where the pin end wall thickness and,therefore, the ring thickness are thin relative to the pipe bodythickness, forming the ring thicker than the pin end wall thicknessimproves strength and stability, thus allowing higher loads to becarried by the same material.

The predominantly flexural stresses induced in the lobate shoulder ringduring installation (due to the reduction of the outer peak diameter andthe radial outward movement of the ring valleys) result in the ring ofthe present invention having a reduced effective hoop stiffness and anincreased radial elastic range, compared to a constant-radius ring shapeunder “shrink fit” radial loading conditions. In this context, effectivehoop stiffness is defined as the change in average radial stressdeveloped on the exterior of a multi-lobe ring caused by a change inradius of a largely cylindrical confining surface (i.e., a surfacehaving a diameter less than the initial outer peak diameter) divided bysaid change in radius (or, stated differently, the average contactstress increase between a multi-lobe ring and a confining surface, perunit decrease in the confining surface radius). Elastic range refers tothe range of confining diameters over which the hoop stiffness of amulti-lobe ring is largely constant.

The effective hoop stiffness and elastic range can be adjusted byselecting the number of lobes, initial outer peak and inner valleydiameters, and ring cross-sectional area. In particular, with respect tothe hoop stiffness and the number of lobes on a ring, increasing thenumber of lobes on a ring with a given diameter requires each lobe tohave a shorter wavelength and, therefore, requires the ring to havegreater hoop stiffness. Generally speaking, the number of lobes on aring will typically be selected for a given connection size and weight,to balance the gripping force with installation load over the tolerancerange allowed by API in combination with other factors such as theinstallation method, risk of thread damage, and material selection.

While the ring is preferably formed from a material similar to that usedto form the coupling, material mechanical properties can be used toadjust the effective hoop stiffness and elastic range of the ring. Inaddition or alternatively, the effective hoop stiffness and elasticrange of the ring can be adjusted by forming the lobes of the ring to benon-symmetrical. Varying lobe shape may be used as another means tocontrol effective hoop stiffness and elastic range to further optimizethe gripping capacity of the ring. In particular, if the lobe shapes arenot all similar, the lobe valleys will not tend to expand at the samerate when the peaks are forced to compress under confinement in thecoupling. As an example, it might be useful to use a ring havingalternating short and long wavelengths to provide higher gripping forceover a greater elastic range of radial interference.

It is to be understood that although the thread element of theillustrated embodiment of the shoulder ring is formed continuouslyaround the circumference of the ring, such that the effective hoopstiffness is substantially not dependent on the circumferential locationof the lobe peaks and valleys, a ring can be formed such that the threadelement is non-continuous around the circumference of the ring, and assuch the lobes of the ring can be aligned so as to take advantage of theopportunity to optimize hoop stiffness and elastic range for thespecific application. By configuring the ring so that the threadelements are located on the flanks of the lobes, rather than at thepeaks and valleys, hoop stiffness is decreased because of the relativelylarge flexural stresses at the peaks and valleys during installation, ascompared to the flanks.

It will be appreciated by persons skilled in the art that known stressanalysis techniques such as the finite element method (FEM) may beadvantageously used to optimize the selection of ring design parameters.

Referring to FIG. 7, in one embodiment the effective frictional capacityor gripping force provided by a ring 10 b capable of exerting a givenradial force is increased by roughening or texturing the ring's outersurface 14 b. The roughening or texturing may be provided in variousways such as knurling or machining or directional teeth, and may beprovided in combination with hardening. Simple V-shaped grooves 19, asshown, have provided substantially higher effective frictioncoefficients than obtained with smooth surfaces, and may be economicallymanufactured (such as cutting by circumferential machined grooves in thering exterior surface 14 b). Preferably, the outer surface of the ringis roughened prior to forming of the lobes.

Referring still to FIG. 7, as a further means to improve the grippingforce of the ring of the present invention within a coupling, a portionof the outer surface 14 b can be shaped generally frustoconically toflare outwards towards face 12 b to follow the coupling box taper. Inparticular, to facilitate installation into a coupling preferably aboutone half of the length of the ring is made of generally uniformthickness. About half of the ring has an outer surface which flaresoutwardly toward face 12 b such that the thickness of the ring isgradually increased from face 11 b to face 12 b of the ring 10 b. Thiscauses the ring to have a generally frustoconical shape covering all ora portion of the outer surface 14 b and substantially matching the taperof the box coupling. Thus when the ring is properly installed in atapered coupling, the field end 12 b of the ring 10 b is in contact withthe field end threads of the coupling 30. The inner surface 13 bpreferably remains generally parallel to the axis of the connectionalong the entire length of the ring 10 b. This embodiment accommodatesinstallation of the ring into the coupling and past the coupling'sminimum center diameter, but provides more conformable contact betweenthe frustoconical portion on the outer surface 14 b of ring 10 b and theinside surface 32 of the coupling box (which will usually be the fieldend box 35″).

Referring still to FIG. 7, a further increase in torque capacity can begained, particularly from API connections of thinner wall tubulars, byshaping one or both of end faces 11 b and 12 b of ring 10 b with aconvex frustoconical profile. In particular, the ends can be formed toslope back from the inner edge to the outer edge providing areverse-angle shoulder on which pin ends 37′ and 37″ bear when reactingtorque. This will tend to prevent the pin end from sliding inward underapplication of high load. Instead, the pin end will be forced radiallyoutwards causing it to pinch between the ring and the coupling, thusfurther increasing the torque capacity of the connection. To functionproperly with this configuration, the strength of ring 10 b as a resultof thickness or material properties must be sufficient to support thestresses at the thinner inner edge.

While a ring having both a roughened frustoconical outer surface andfrustoconical end faces is shown in FIG. 7, it is to be understood thateach of these modifications can be used independently in a particularring, as desired.

The range of diameters allowed at the center of couplings manufacturedto API specifications is large compared to the available elastic rangeof constant-radius steel rings, but is readily accommodated by rings ofthe present invention having a minimum of two but preferably three ormore lobes, while simultaneously controlling the average radial stressto balance installation load against gripping force. This can beaccomplished while preferably ensuring that the installed inner diameterdoes not fall below the minimum drift diameter required by theapplication for the rings installed in maximum internal diametercouplings, and preferably without substantially engaging the inelasticcompressive hoop response of the ring when installed in a minimumdiameter coupling.

Although in the embodiment shown in FIG. 4 the thread element 17 on ring10 bears the same thread profile as the male threads on the outsidesurface of both pins 34′ and 34″, it is to be understood that the threadprofile can be adjusted as desired to facilitate or enhance ease ofinstallation or operational performance.

FIG. 8 illustrates an alternative embodiment of the shoulder ring of thepresent invention, adapted to eliminate any need for rotation or torqueapplication during installation. In accordance with this embodiment,ring 10 c has a thread element 17 c with a low stab flank angle and alow thread height. Installation of this ring may be accomplished byforcing ring 10 c into the coupling by application of axial force to thefield end 12 c of the ring 10 c. By virtue of shoulder ring 10 c havingat least two (and preferably three or more) lobes, ring 10 c will deformelastically, in the radial direction, as thread element 17 c is pressedagainst the coupling's internal thread structure, such that threadelement 17 c will engage the coupling's thread structure.

Two possible post-installation configurations for a ring of this designare illustrated in FIGS. 8 and 9. In the first configuration, shown inFIG. 8, thread element 17 c is engaged within the threads on the insidesurface 32 of coupling 30. In the second configuration, shown in FIG. 9,thread element 17 c is in contact with the crests of the female threadof the field end box 35″ of coupling 30. In this configuration, ring 10c is axially retained within coupling 30 primarily by virtue of radialcontact forces between thread element 17 c and the thread crests and theresulting frictional resistance. However, should ring 10 c becomeaxially dislodged from the position shown in FIG. 9, thread element 17 cwill tend be urged into engagement (or further engagement) with thecoupling's internal thread structure to provide additional axialretention force and thus prevent the ring from backing out further.

In another embodiment of the invention, as shown in FIG. 10, ring 10 din its unstressed state has a circular shape with a constant radius andprofile about the circumference (i.e., no lobes). Ring 10 d has threadelement 17 d on outer surface 14 d. The outside diameter of ring 10 d isselected such that a coupling having the smallest diameter allowed bythe specified tolerances for the coupling, thus minimizing requiredinstallation torque. Installation of ring 10 d into a coupling 30 isaccomplished by engaging thread element 17 d with the threads of thefield end coupling box 35″ and rotating ring 10 d until the mill end 11d of ring 10 d contacts end 37′ of mill end pin 34′; this will ensuresubstantially uniform and unrestricted axial load and torque transferbetween pin ends 37′ and 37″ upon installation of the field end pin 37″.

Various means can be used to position ring 10 d in coupling 30,including installation by hand. Using this installation method, ring 10d may be threaded into coupling 30 as far as possible by hand, withsubsequent rotation of the field end pin being effective to rotate ring10 d further into coupling 30.

Tools for Installing Shoulder Ring with Thread Element

A preferred embodiment of the shoulder ring installation tool of thepresent invention is shown in FIGS. 11 and 12. Referring now to FIG. 11,installation tool 50 comprises a gripping collet 51 with upper end 52and lower end 53 carrying collet fingers 53 f coaxially mounted outsideand closely fitting with torque application shaft 54 with upper end 55and lower end 56. Lower end 53 of collet 51 has a peripheral grippingsurface 57 closely fitting and carrying ring 10. Torque applicationshaft 54 has a torque grip activation mechanism 58 at bottom end 56, anda torque application handle 59 at upper end 55. Torque is applied totorque application handle 59 at the top end 55 of torque applicationshaft 54.

Referring now to FIG. 12, torque grip application mechanism 58 isprovided by arranging the close-fitting interface between the inside ofcollet fingers 53 f and the outside surface of bottom end 56 of torqueapplication shaft 54 as facetted interface 60 (illustrated in FIG. 12 ashaving 16 facets and 8 collet fingers 53 f), so that upon application oftorque to handle 59, gripping surface 57 of gripping collet 51 tends tobe forced radially outwardly by the mechanics of faceted interface 60 oftorque grip activation mechanism 58 to grip the inside surface 13 ofring 10. Referring again to FIG. 11, the ring 10 is rotated intoposition so that its mill end 11 contacts the end 37′ of mill end pin34′. Removing the applied torque will release the frictional contactbetween gripping surface 57 of gripping collet 51 and the inside surface13 of ring 10. As may be required, reverse torque can be applied, alsoactivating the grip mechanism for ring extraction.

In another embodiment, as shown in FIG. 13, installation tool 70comprises a frustoconical grip 71 with lower end 72, upper end 73, outersurface 74, and inside surface 75, plus a torque application shaft 76with upper end 77 and lower end 78. Installation tool 70 is operated byforcing ring 10 over the lower end 72 of the frustoconical grip 71either by hand or using an axially-oriented hydraulic ram assembly (notillustrated). The inside surface 13 of ring 10 contacts the outsidesurface 74 on the lower end 72 of the frustoconical grip 71. Theresulting radially outward force on the lobe valleys of ring 10 inducesa radially outward movement of the valleys and a radially inwardmovement of the peaks so that ring 10 becomes substantially round. Thering 10 can then be threaded into the field end box 35″ on the coupling30 so that the mill end 11 of ring 10 contacts the end 37′ of mill endpin 33′. Tool 70 is then pulled axially out of the box either manuallyor by using an axially-oriented hydraulic ram assembly (notillustrated), allowing the ring 10 to return, to the extent allowed bythe inside surface 32 of the coupling 30, to a lobate shape.

In a further embodiment as shown in FIGS. 14 and 15, installation tool90 comprises a torque application shaft 91 with upper end 92 and lowerend 93, and a lobed grip 94 with upper end 95, lower end 96, and outersurface 97. Referring now to FIG. 15, the outside surface 97 of lobedgrip 94 is designed to be in mating engagement with the inside surfaceof the lobes of ring 10. Referring again to FIG. 14, rotation and torqueare then applied, manually or with mechanical assistance, to torqueapplication shaft 91 to screw the ring into the center of the coupling.As ring 10 is advanced into the coupling 30 and the ring lobes engagethe coupling, tangential drag is induced between the ring 10 andcoupling 30 and reacted through the interaction of lobed grip 94,tending to rotate or advance the lobes of outside surface 97 relative tothose of ring 10, which action feeds back to reduce the lobe amplitudeof ring 10 and reduce the drag. As the ring approaches the center of thecoupling, the lobe amplitude thus tends to become smaller, and slippagebetween the ring and the gripping surface becomes imminent if the ringbecomes excessively round. Rings and lobe amplitude are thereforearranged to prevent this occurrence over the range of coupling diametertolerance allowed by specifications for the coupling.

Outwardly Crimpable Shoulder Ring

In an alternative embodiment, the shoulder ring of the present inventionis adapted and configured such that it can be plastically deformed byapplication of radially outward forces applied to the ring after initialplacement within a coupling, thereby providing axial retention withinthe coupling by way of an interference fit between the outer surfaces ofthe ring and the internal thread structure of the coupling. Inaccordance with this embodiment, and as illustrated in FIG. 16, ring 10e has a substantially cylindrical shape and is made from a suitablystrong yet ductile metal, and has outer surface 14 e, inner surface 13e, upper end face 11 e, and lower end face 12 e. Outer surface 14 e ofring 10 e is shown to be smooth; however, it will be understood thatroughness (e.g., knurling, threading, or grooving) can be added to outersurface 14 e to enhance gripping characteristics. As best seen in FIG.17, the inner surface 13 e of ring 10 e is preferably profiled to definea pair of frustoconical surfaces 18 e′ and 18 e″, arranged such that theradial thickness of ring 10 e is less at its longitudinal center pointthan at end faces 11 e and 12 e. Referring to FIG. 17, ring 10 e isshown in cross-section centrally disposed within the bore of ataper-threaded coupling 30 threaded onto pin 34, as ring 10 e wouldappear prior to plastic deformation.

Referring now to FIG. 18, shoulder ring 10 e is again shown in coupling30 but now as it would appear after deformation. Upon comparison of theshoulder ring's pre-deformation and post-deformation forms, as shown inFIG. 17, it will be apparent to one skilled in the art that theoriginally frustoconical internal surfaces 18 e′ and 18 e″ will tend tobecome cylindrical after deformation. Correlatively, the originallycylindrical outer surface 14 e will tend to become shaped as afrustoconical pair of surfaces (or, perhaps, as a single, longitudinallyconcave surface), closely matching and interlocking with the shape ofthe tapered coupling threads. Such interlocking facilitates axialretention, while maintaining a relatively smooth bore so as not toencroach on the drift diameter of the casing string.

Axial retention can be further enhanced by controlling ring deformationso as to induce an interference fit either mechanically or thermally.Mechanical interference can be enhanced by selecting the elastic moduliand yield strengths of ring 10 e and coupling 30 such that uponapplication of sufficient outward radial force to internal surface 13 e,the elastic rebound or elastic strain induced in coupling 30 exceedsthat induced in ring 10 e, resulting in a residual interference fit uponrelease of the outward radial force. An interference fit can also bepromoted or enhanced by way of a thermally-induced shrink fit, inaccordance with methods well known in the art, by selectivelycontrolling the relative temperatures of ring 10 e and coupling 30during ring deformation so that the thermal strain of the coupling 30exceeds that of ring 10 e.

It is to be understood that shoulder ring 10 e is not restricted to theparticular configuration shown in FIG. 16, and that one or moreadditional features (including but not limited to those featuresdescribed herein with respect to other embodiments of the shoulder ring)can be added to enhance axial retention of ring 10 e within thecoupling, and/or to facilitate ring installation.

Tools for Installing Outwardly Crimpable Shoulder Ring

FIG. 19 illustrates an installation tool for installing outwardlycrimpable shoulder rings generally of the type described above withreference to FIGS. 16-18. As shown in FIG. 19, installation tool 110 hasa top end 111 and a bottom end 112, plus a mandrel component 113 whichextends axially along the length of the tool. The uppermost portion ofmandrel 113 is substantially cylindrical, with a threaded connection 117at upper end 115. This cylindrical portion of mandrel 113 transitions toa frustoconical section 116 which tapers or flares outwardly towardlower end 114.

Generally disposed around the outside surface 118 of mandrel 113 is acollet component 120. The collet 120 has an upper end 121 with axialload application mechanism 130, and a lower end 122 with a plurality ofcircumferentially arrayed collet die fingers 124 (sixteen in theillustrated exemplary embodiment) which are slidingly engageable withthe alternately cylindrical or frustoconical outside surface 118 ofmandrel 113. The collet die fingers 124 have grooves along their outersurfaces 125 which are adapted to grippingly engage the inside surface13 e of ring 10 e. The load application mechanism 130—anaxially-oriented hydraulic ram, in the illustrated embodiment—uses themandrel 113, the collet 120, and a threaded seal ring 131 to form afluid chamber 127. Threaded seal ring 131 has upper end 132, lower end133, thread element 136, and seal groove 137 on inside surface 134,which threadingly and sealingly engages the outside surface 118 ofmandrel 113, and a generally cylindrical outside surface 135 withintegral seal groove 138, which slidingly and sealingly engages theinside surface 129 of collet 120. Pressure applied to fluid chamber 127(via fluid port 128 in seal ring 131) induces an axial upward movementof the mandrel 113 relative to the collet 120, which in turn, induces aradial outward movement of the dies 124.

It is to be understood that while the axial load application mechanism130 is shown and described herein as a hydraulic ram, it is notrestricted to this design and as such could be provided in the form ofother suitable and known mechanisms (such as a jack screw), withoutdeparting from the concept of the present invention.

As axial load is applied, the ring 10 e is elastically and plasticallydeformed until the outer surface 14 e is brought into contact with theinner surface 32 of coupling 30 so as to effect an interference fit.Additional radially outward force can be applied to the inside surface13 e of the ring 10 e to further plastically deform the ring 10 e andpush coupling 30 further radially outward, thus effecting aninterlocking fit by localized plastic deformation of ring 10 e into thethread structure of coupling 30.

As previously indicated, the elastic moduli and yield strengths of ring10 e and coupling 30 can be selected such that upon application ofsufficient outward radial force to internal surface 13 e of ring 10 e,the elastic rebound or elastic strain induced in coupling 30 exceedsthat induced in ring 10 e, resulting in a residual interference fit uponrelaxation of the outward radial force. The residual radial interferenceis reacted as a contact force between the minimum diameter of the insidesurface 32 of coupling 30 and the maximum diameter of the outsidesurface 14 e of shoulder ring 10 e, which contact frictionally resiststhe ring 13 e from being displaced from the coupling 30.

It is to be understood that while the embodiment of the installationtool shown in FIG. 19 and described above applies radially outward forceby means of a collet/mandrel assembly, the tool is not limited to thatmeans of inducing ring deformation. To provide just one non-limitingexample, the required radial installation load can be generated byalternative means such as radially-oriented, hydraulically-drivenpistons. It will further be appreciated that the effective use of theinterference-fit method of installing a shoulder ring, usinginstallation tools as described or similar thereto, is not dependent onthe use of shoulder rings of specific configuration. Although beneficialresults may be achieved using shoulder rings with frustoconical insidesurfaces as described above, the described installation method andinstallation tool are also adaptable for use with outwardly-crimpableshoulder rings of other configuration, including rings of substantiallycylindrical form.

It will be readily appreciated by those skilled in the art that variousmodifications of the present invention may be devised without departingfrom the essential concept of the invention, and all such modificationsare intended to come within the scope of the present invention.

In this patent document, the word “comprising” is used in itsnon-limiting sense to mean that items following that word are included,but items not specifically mentioned are not excluded. A reference to anelement by the indefinite article “a” does not exclude the possibilitythat more than one of the element is present, unless the context clearlyrequires that there be one and only one such element.

What is claimed is:
 1. A method for installing a substantiallycylindrical shoulder ring in a threaded pipe coupling, said methodcomprising the steps of: (a) providing a shoulder ring installation toolhaving a mandrel adapted to receive a cylindrical shoulder ring, withsaid tool further having means for uniform application of radiallyoutward force to said ring; (b) positioning a cylindrical shoulder ringon the mandrel; (c) inserting the mandrel into the cavity of a pipecoupling until the shoulder ring is approximately centered within thecoupling; and (d) actuating the installation tool to exertradially-outward force to the ring sufficient to plastically deform thering and effect an interference fit with an inner surface of thecoupling, whereby the ring is axially retained within the coupling.
 2. Amethod for installing a substantially cylindrical shoulder ring in athreaded pipe coupling, said method comprising the steps of: (a)providing a shoulder ring installation tool having a mandrel adapted toreceive a cylindrical shoulder ring, with said tool further having meansfor uniform application of radially outward force to said ring; (b)positioning a cylindrical shoulder ring on the mandrel; (c) insertingthe mandrel into the cavity of a pipe coupling until the shoulder ringis approximately centered within the coupling; and (d) actuating theinstallation tool to exert radially-outward force to the ring sufficientto plastically deform the ring and effect an interlocking fit with aninner surface of the coupling, whereby the ring is axially retainedwithin the coupling.